1. Field of the Invention
The present invention relates to an apparatus and method for the fragmentation, sterilization, separation, and recovery of recyclable materials from solid waste, such as solid municipal waste, as well as other bio mass materials. The solid waste material is introduced into a rotatable, "kiln-like" pressure vessel with the infusion of a controlled amount of fluid, preferably steam, where it is subjected to elevated temperatures and pressures and mechanical forces exerted within the vessel. Jets of high pressure fluid are used to induce a cutting/agitation action on the waste material as it moves through the pressure vessel.
2. Description of Related Art
Great quantities of solid waste materials, particularly municipal solid waste (MSW), are generated and collected regularly in both rural and urban areas of the United States and other developed countries. Suitable disposal methods are required for such waste. The customary solutions for the disposal of such solid waste materials has been to either deposit them into landfills or to separate the inorganic and organic components and incinerate the organic components, either directly, or in the form of fuel derived from the organic components. However, such disposal methods are becoming increasingly expensive and/or environmentally undesirable.
Processing of municipal solid waste (MSW) to produce solid fuel products suitable for combustion in steam boilers of electric power plants is known and in commercial use.
However, such solid fuel products have serious disadvantages, including an undesirably high moisture content, a high ash content and relatively low heat value. Improvements and innovations in solid waste treatment processes are needed because of the growing economic and environmental needs to recycle and reuse as much of the increasing amounts of municipal solid waste (MSW) material that are produced.
Consequently, the patent literature has been replete with various disclosures concerning MSW management, offering all sorts of methods and techniques to deal with this exploding waste management problem.
One type of technology that is of particular interest for the separation and recovery of municipal waste components is an in-vessel technology that utilizes a pressure vessel for holding the waste where it is rotated, pressurized, and heated with steam while simultaneously being mechanically agitated and moved through the vessel by an extruding action. The extruding action is achieved by a rotatable extruder mechanism in the pressure vessel that forces the solid waste material through one or more constricted areas at the discharge end of the pressure vessel. Such a method, and some of its variations, are disclosed in U.S. Pat. Nos. 4,342,830; 4,450,495; 4,844,351; 5,190,944; and 5,361,994 all to Holloway and all of which are incorporated herein by reference.
While some of the above methods have met with varying degrees of technical and commercial success, they still suffer from inherent problems. For example, in-vessel treatment has become well known in the art and affords some advantage over landfilling and incinerating, but it is very time and labor intensive. It generally does not lead to the cost-effective or efficient recovery of the utilizable inorganic components of a typical municipal solid waste material. Therefore, "pre-process" classification, segregation and removal of the inorganic portions (metals, plastics, glass, etc.) of the municipal solid waste to be treated is usually necessary. These classification and separation techniques are well known in the art, such as trommel separation or size classification of solid components, air classification systems for plastics, spectrographic segregation for glass, and magnetic and eddy current separation for ferrous and non-ferrous metals. The utilization of conventinoal in-vessel composting methodology, without some form of "pre-process" classification and removal of these inorganic components, contaminates the inorganic components during treatment making the recovery of such components more difficult and substantially depreciating their value. Other difficulties incumbent upon in-vessel treatment of solid waste include the protracted length of time the waste material must remain in the vessel (residence time) for treatment to be completed; and the relatively high moisture content of the end-product. This high moisture content inhibits the separation of the organic components from the inorganic components and necessitates additional drying of the end-product material for further processing. Additional drying is particularly difficult in the in-vessel processes that introduce a relatively high volume of moisture into the vessel in order to fluidize the material.
These noted deficiencies are overcome by the practice of the present invention that eliminates the need for any "pre-process" classification of the mixed municipal solid waste and does not instill any extraneous or unnecessary water into the system. The moisture content of the end-product exiting the vessel of the present invention will not exceed 30%, preferably it will not exceed 20%, by weight. The present process has the additional advantage of producing an end-product from biomass that is relatively dry and readily utilizable for numerous products, including a fuel product. The present invention also has the advantage of sterilizing the inorganic components of municipal solid waste and rendering such components readily recoverable from the waste stream because of the removal of labels and coatings from them.